1. Field of the Invention
The present invention relates to an ink jet recording apparatus, a head drive and control device, a head drive and control method, and an ink jet head.
2. Description of the Related Art
Employed in an ink jet head recording apparatus used as an image recording apparatus (an imaging apparatus) such as a printer, a facsimile machine, a copier, or a plotter is an electrostatic ink jet head including nozzles for ejecting ink droplets, ink channels (also referred to as ejection chambers, pressure chambers, liquid pressure chambers, or liquid chambers) communicating with the nozzles, diaphragms each forming a part of wall faces inside a corresponding one of the ink channels, and electrodes opposing the diaphragms so that the ink droplets are ejected from the nozzles by pressurizing ink in the ink channels by deforming and moving the diaphragms by means of electrostatic force.
The electrostatic ink jet head employs electrostatic force, storing smaller energy in the same volume compared with another type of ink jet head using piezoelectric elements or calorific resistances as actuator means. Therefore, the electrostatic ink jet head can reduce power consumption and operates at a higher rate by simultaneously driving numerous nozzles. That is, an ink jet head other than that of an electrostatic type ejects ink droplets by means of energy several hundred or thousand times as large as the kinetic energy of the ink droplets, so that heat is generated from extra energy in the head or a driver IC (a driving circuit), thus setting a limit to the number of nozzles operable at the same time or a driving frequency due to the effect of heat reserve.
Since an ink jet recording apparatus is required to achieve higher image quality and a higher recording rate, it is necessary for the ink jet recording apparatus to eject finer ink droplets at a higher frequency. However, due to a limit to an ejection frequency, it is difficult to perform high-speed recording only with fine ink droplets. Therefore, it has been desired of the ink jet recording apparatus to perform a multi-level operation of ejecting different amounts of ink droplets from the same nozzle.
In this case, a multi-level driving method is prevented from being established with the electrostatic ink jet head since it is difficult, compared with other methods, to control ink droplet ejection power with the multi-level driving method due to the direction of the electrostatic force, which can generate only attraction to attract the diaphragms toward the electrodes, and the nonlinearity of the electrostatic force, which is inversely proportional to the square of a distance between the diaphragms and the electrodes.
Further, there is a recent trend toward a smaller nozzle diameter to eject finer ink droplets, which entails a problem that nozzle clogging occurs more easily with the smaller nozzle diameter. Therefore, it is desired to eject ink droplets of a considerable size and a finer size with respect to a nozzle diameter.
Therefore, as a conventional electrostatic ink jet head, Japanese Laid-Open Patent Application No. 8-72240 discloses an ink jet recorder including a plurality of electrodes for ink droplet ejection which electrodes oppose one diaphragm and ejecting ink droplets of an amount corresponding to a gradation signal by changing the number of electrodes to be driven in accordance with the gradation signal.
Further, Japanese Laid-Open Patent Application No. 9-39235 discloses an ink jet head which has electrodes opposed to diaphragms and each formed to have a step-like structure so that large, middle, and small gaps are formed between the electrodes and corresponding diaphragms and ejects a variable amount of ink droplets by changing the deformation of each diaphragm by determining a level to which each diaphragm is deformed;
Further, Japanese Laid-Open Patent Application No. 9-254381 discloses an ink jet recording apparatus ejecting fine ink droplets by being drivable at a high frequency and shortening the natural frequency of ink by restricting the deformation of the diaphragms by forcibly placing diaphragms in contact with corresponding electrodes by applying a second driving voltage (an auxiliary voltage) lower than a first driving voltage at a timing when the diaphragms deformed by the applied first voltage approach the electrodes.
However, providing the electrodes for ink droplet ejection opposing the diaphragm as disclosed in Japanese Laid-Open Patent Application No. 8-72240 requires driving the electrodes independently of one another. This increases the number of interconnection lines and drivers to complicate an apparatus structure, thus resulting in a larger apparatus size and higher production costs.
Further, forming the electrodes opposing the diaphragms so that the electrodes each have a step-like structure so that large, middle, and small gaps are formed between the electrodes and corresponding diaphragms as disclosed in Japanese Laid-Open Patent Application No. 9-254381 requires a complicated head structure and production process, thus resulting in higher production costs. In order to drive a head having such a structure, it is necessary to apply a complicated driving waveform varying a driving voltage value. This complicates a driving circuit structure, thus causing higher production costs.
Furthermore, with respect to the ink jet recording apparatus disclosed in Japanese Laid-Open Patent Application No. 9-254381, it cannot be explained technically that finer droplets can be ejected at the shorter natural frequency, and practically, it is impossible to eject fine droplets with a droplet velocity being maintained.
It is a general object of the present invention to provide an ink jet recording apparatus, a head drive and control device, a head drive and control method, and an ink jet head in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide an ink jet recording apparatus, a head drive and control device, a head drive and control method, and an ink jet head that enable fine droplets to be ejected by a simple structure.
The above objects of the present invention are achieved by an ink jet recording apparatus including: an ink jet head including a nozzle for ejecting an ink droplet, an ink channel communicating with the nozzle, a diaphragm forming a part of wall faces of the ink channel, and an electrode opposing the diaphragm, the diaphragm being deformed by electrostatic force so that the ink droplet is ejected from the nozzle; and a part applying to the ink jet head a first driving signal for generating the electrostatic force for ejecting the ink droplet from the nozzle and a second driving signal for controlling deformation of the diaphragm, the second driving signal being applied after a predetermined period of time passes since application of the first driving signal.
According to the above-described ink jet recording apparatus, the diaphragm is deformed toward the electrode at a timing and by an amount for ejecting a desired amount of ink by the application of the first driving signal, and thereafter, the deformation of the diaphragm is controlled by application of the second driving signal. Thereby, a fine ink droplet is ejected from the nozzle.
Additionally, in the above-described ink jet recording apparatus, the second driving signal may be applied to the electrode or to a substrate on which the electrode is formed, or the ink jet head may further include an additional electrode opposing the diaphragm and electrically separated from the electrode and the second driving signal may be applied to the additional electrode.
Thereby, the above-described ink jet recording apparatus has its electrode structure and/or driving circuit structure simplified.
The above objects of the present invention are also achieved by a head drive and control device for driving and controlling an ink jet head including a nozzle for ejecting an ink droplet, an ink channel communicating with the nozzle, a diaphragm forming a part of wall faces of the ink channel, and an electrode opposing the diaphragm, the diaphragm being deformed by electrostatic force so that the ink droplet is ejected from the nozzle, which head drive and control device includes a first part applying to the ink jet head a first driving signal for generating the electrostatic force for ejecting the ink droplet from the nozzle and a second driving signal for controlling deformation of the diaphragm, the second driving signal being applied after a predetermined period of time passes since application of the first driving signal.
According to the above-described head drive and control device, the diaphragm is deformed toward the electrode at a timing and by an amount for ejecting a desired amount of ink by the application of the first driving signal, and thereafter, the deformation of the diaphragm is controlled by application of the second driving signal. Thereby, a fine ink droplet is ejected from the nozzle.
Additionally, the above-described head drive and control device may further include a second part generating the first and second driving signals in time series.
Thereby, the above-described head drive and control device can selectively perform application of only the first driving signal or application of both of the first and second driving signals with a simple structure.
The above objects of the present invention are also achieved by a method of driving and controlling an ink jet head including a nozzle for ejecting an ink droplet, an ink channel communicating with the nozzle, a diaphragm forming a part of wall faces of the ink channel, and an electrode opposing the diaphragm, the diaphragm being deformed by electrostatic force so that the ink droplet is ejected from the nozzle, which method includes the step of applying a second driving signal for controlling deformation of the diaphragm to the ink jet head after a predetermined period of time passes since application of a first driving signal for generating the electrostatic force for ejecting the ink droplet from the nozzle.
According to the above-described method, the diaphragm is deformed toward the electrode at a timing and by an amount for ejecting a desired amount of ink by the application of the first driving signal, and thereafter, the deformation of the diaphragm is controlled by application of the second driving signal. Thereby, a fine ink droplet is ejected from the nozzle.
The above objects of the present invention are also achieved by an ink jet recording apparatus including: an ink jet head including a nozzle for ejecting an ink droplet, an ink channel communicating with the nozzle, a diaphragm forming a part of wall faces of the ink channel, and an electrode opposing the diaphragm, the diaphragm being deformed by electrostatic force so that the ink droplet is ejected from the nozzle; and a first part applying to the ink jet head a first driving signal for generating the electrostatic force so that the diaphragm is deformed to contact the electrode and a second driving signal having a peak value higher than that of the first driving signal, the second driving signal being applied before the diaphragm starting restoration by stopping application of the first driving signal reaches an equilibrium position of the diaphragm.
According to the above-described ink jet recording apparatus, when the application of the first driving signal is stopped, the diaphragm suddenly starts restoration to generate a pressure wave so that a satellite ink droplet is ejected from the nozzle. Thereafter, by applying the second driving signal, the restoring force of the diaphragm is weakened so that a main ink droplet is prevented from being ejected from the nozzle. Thereby, the satellite ink droplet is ejected as a finer ink droplet.
The above object of the present invention are also achieved by a head drive and control device for driving and controlling an ink jet head including a nozzle for ejecting an ink droplet, an ink channel communicating with the nozzle, a diaphragm forming a part of wall faces of the ink channel, and an electrode opposing the diaphragm, the diaphragm being deformed by electrostatic force so that the ink droplet is ejected from the nozzle, which head drive and control device includes a part applying to the ink jet head a first driving signal for generating the electrostatic force so that the diaphragm is deformed to contact the electrode and a second driving signal having a peak value higher than that of the first driving signal, the second driving signal being applied before the diaphragm starting restoration by stopping application of the first driving signal reaches an equilibrium position of the diaphragm.
According to the above-described head drive and control device, when the application of the first driving signal is stopped, the diaphragm suddenly starts restoration to generate a pressure wave so that a satellite ink droplet is ejected from the nozzle. Thereafter, by applying the second driving signal, the restoring force of the diaphragm is weakened so that a main ink droplet is prevented from being ejected from the nozzle. Thereby, the satellite ink droplet is ejected as a finer ink droplet.
The above objects of the present invention are further achieved by an ink jet including: a nozzle for ejecting an ink droplet; an ink channel communicating with the nozzle; a diaphragm forming a part of wall faces of the ink channel; a first electrode opposing the diaphragm to which first electrode a first driving signal for generating electrostatic force is applied, the electrostatic force deforming the diaphragm so that the ink droplet is ejected from the nozzle; and a second electrode to which a second driving signal for controlling deformation of the diaphragm is applied after a predetermined period of time passes since application of the first driving signal.
According to the above-described ink jet head, since the second driving signal for controlling the deformation of the diaphragm is applied to the second electrode other than the first electrode, a circuit structure for application of the second driving signal is simplified.